The present invention relates to liquid drainage systems.
During catheterization of a patient, a distal end of a catheter is passed through the urethra until a drainage eye in the distal end of the catheter is located in the patient's bladder. An upstream end of a drainage tube is connected to a proximal end of the catheter located outside the patient's body, and a downstream end of the drainage tube communicates with a collection receptacle. Thus, urine from the bladder drains through the catheter drainage eye, a lumen in the catheter, and through a lumen in the drainage tube to the receptacle for collection therein.
During drainage, solid columns of urine form in the drainage tube which create a negative pressure in the drainage tube. In order to drain the urine, air must rise through the column of urine to the top of the column which is frequently a relatively slow process. Hence, the urine columns are often found in the drainage tube, and are undesirable for a number of reasons. First, the pooled urine in the drainage tube provides an easy pathway for the migration of bacteria up the drainage tube toward the patient's bladder. Second, the volume of urine in the collection receptacle is often measured by hospital personnel, and the measured volume does not include the urine located in the drainage tube resulting in an inaccurate measurement. Third, the negative pressure created by the urine columns may cause lesions in the patient's bladder.
It is possible to provide a vent for the drainage tube in order to permit passage of air from the atmosphere to the lumen of the drainage tube, thus alleviating the negative pressure in the drainage tube and causing rapid drainage through the drainage tube. Of course, it is necessary to provide a filter for such a vent in order to remove bacteria from the air which passes into the drainage tube, since the closed drainage system would otherwise become contaminated. However, it has been found that repeated contact of urine against the filter causes the filter to close, thus rendering the vent inoperable and again causing formation of urine columns and a negative pressure in the drainage tube.